* Only one NameNode is possible to configure.
* Secondary NameNode was to take hourly backup of MetaData from NameNode.
* It is only suitable for Batch Processing of a vast amount of Data, which is already in the Hadoop System.
* It is not ideal for Real-time Data Processing.
* It supports up to 4000 Nodes per Cluster.
* It has a single component: JobTracker to perform many activities like Resource Management, Job Scheduling, Job Monitoring, Re-scheduling Jobs etc.
* JobTracker is the single point of failure.
* It supports only one Name No and One Namespace per Cluster.
* It does not help the Horizontal Scalability of NameNode.
* It runs only Map/Reduce jobs.
